The central hypothesis of this project is that a developing joint or skeletal anlage from one species may serve as a morphogenic scaffold for chondrocytes from another species. The anlage will be rendered devoid of innate viable chondrocytes and seeded with chondrocytes from another organism for culture. The source of the viable chondrocytes and thus the cell surface antigens within this engineered growing joint or anlage could therefore be selected. Transplanatation of the engineered construct back into the organism from which the viable chondrocytes had been obtained would be useful in orthopedic and maxillofacial reconstructive surgery. It is our belief that the information obtained from the proposed studies will be translated for clinical application within a short period of time. Our hypothesis will be tested with three major Specific Aims (SA): SA I: The effect of developmental age and thus matrix composition of developing joint scaffolds on the permeation of xenogeneic chondrocytes throughout them will be characterized. SA II: The in vitro growth of engineered joints will be measured. SA III: The fate of in vitro engineered joints in surgical models will be assessed. These studies will first use bovine chondrocytes/chick joint scaffolds because of their low cost. Once technical parameters are defined, mouse chondrocytes/rat joint scaffolds and pig chondrocytes/pig joint scaffolds will be used in preparation for in vivo models. Methods for the in vitro studies include histomorphometric, biochemical and molecular analysis of chondrocyte function. In vivo fate of engineered joints will be assessed in our model of murine joint transplantation and will be further verified in the pig.